This invention relates generally to semiconductor devices and more particularly to surface-passivated semiconductor devices, adaptable for high-performance applications, and to methods of fabricating such items.
Since the commercial advent of semiconductor products, there has been an intense and continuing search for ways of increasing their reliability, especially under conditions of high electrical and environmental stress. Surface passivation techniques have received considerable attention in this quest; and passivation has been practiced in the past by means of organic coatings, glass compositions, and both deposited and thermally formed films of silicon dioxide. More recently, coatings of both silicon nitride and polycrystalline silicon doped with oxygen have been proposed.
Each of the prior art schemes has disadvantages. Organic passivations require skilled workers for their application, present hazards to the factory environment, and fail to exhibit optimized electrical properties at the interface with the semiconductor body proper, due at least in part to poor molecular bonding with the substrate material. Glass passivations, on the other hand, usually have limited tolerance to processing chemicals, are sensitive to assembly procedures, and sometimes display erratic electrical behavior. Silicon dioxide passivation films are mechanically weak, have extremely unstable surface charges, and are susceptible to undesirable migration of such alkali metal ions as sodium ion, resulting in failure of the electrical isolation. Silicon nitride passivation coatings are difficult to etch in a sharp pattern and exhibit undesirable dipolar effects with concomittant reduction in reverse voltage properties. Finally, simple oxygen-doped polycrystalline silicon passivations permit unacceptable electrical leakage upon prolonged exposure of the coated semiconductor device to elevated temperatures.
It is therefore a general object of the present invention to provide a new and improved surface-passivated semiconductor device which overcomes many of the limitations of the prior art and which can be operated in a continuous manner under exacting conditions.
Another object of the invention is to provide a high-performance semiconductor device which includes a multi-layer passivation of semi-insulating character.
Still another object of the invention is to provide a surface-passivated semiconductor device which functions reliably at high operating voltages.
And still another object of the invention is to provide a surface-passivated semiconductor device which counteracts the development of both static and mobile electrical charges in the vicinity of the interface between the passivation layer and the substrate.
A further object of the invention is to provide a new and improved method of surface-passivating semiconductor devices.
A yet further object of the invention is to provide a method of continuously applying a dual-layer passivation coating to semiconductor devices.
These and other objects and features of the invention will become apparent from a consideration of the following descriptions.